1. Field of the Invention
The present invention relates to an opening portion structure of a fuel tank made of a thermoplastic synthetic resin and its fabricating method, particularly relates to an opening portion structure of a fuel tank made of a thermoplastic synthetic resin and its fabricating method for forming a fuel tank main body by subjecting a synthetic resin member having a plurality of layers to blow forming and forming an opening portion integrally with the fuel tank main body.
2. Related Art
Although in a related art, there is used a structure of a fuel tank for an automobile or the like made of a metal, in recent years, there has been used a structure of a fuel tank made of a thermoplastic synthetic resin owing to light-weighted formation of a vehicle, because rust is not generated thereon, the structure is easy to be formed into a desired shape and so on.
In fabricating a fuel tank for an automobile made of a synthetic resin, there has frequently been used a blow forming method owing to an easiness in forming a hollow member. According to the blow forming method, a fuel tank for an automobile is fabricated by constituting a parison of a molten thermoplastic synthetic resin member by a cylindrical shape to be extruded from above, clamping the parison by a die and blowing air into the parison.
The fuel tank is formed with an opening portion for bringing in and out a part to be mounted to inside of the tank. In forming the opening portion, simultaneously with forming a fuel tank main body by blow forming, the opening portion is formed integrally therewith.
As shown in, for example, FIG. 8, a structure thereof is attached with an opening portion 110 and a lid member 140 for closing the opening (refer to, for example, JP-A-2002-187162).
According to a constitution of FIG. 8, a cam lock member 120 for locking the lid member 140 is embedded to a periphery of the opening portion 110, the lid member 140 is clamped by a fixing member 130 in a ring-like shape and the opening portion 110, the fixing member 130 is pressed by the cam lock member 120 to thereby fix the lid member 140. At this occasion, in order to seal an interval between the lid member 140 and the opening portion 110, a seal ring 150 is attached to therebetween. In order to attach the seal ring 150, a groove portion 116 is formed at a face of the opening portion 110 opposed to the lid member 140.
Although a smooth face is needed for the groove portion 116 in order to ensure seal performance, when the groove portion 116 is formed by blow forming, a sufficient smooth face is not provided by only pressing the groove portion 116 to an inner face of a blow forming die by an inner pressure of blow. Further, in order to prevent gasoline from being permeated from an end face of the opening portion 110, it is necessary to thin a wall thickness of the groove portion 116 of the opening portion 110.
However, when a slide die is moved to form the groove portion 116 from a direction orthogonal to the opening portion 110 to compress the groove portion 116 in forming the groove portion 116 in order to form the portion of the groove portion 116 to be thin, since the cam lock member 120 is only embedded at the portion of the opening portion 110, and therefore, there is not a portion of holding the portion of the groove portion 116, a pressure of the compressing die cannot be received and it is difficult to compress the groove portion 116.
Further, the cam lock member 120 is projected from the opening portion 110 in an outer direction, and therefore, it is necessary to ensure a gap between the cam lock member 120 and a peripheral part, a large space is needed, a volume of the fuel tank is reduced, or a structure of the blow molding die becomes complicated.
Further, as shown in FIG. 9, there is also a structure for forming a fuel tank main body 201 by a thermoplastic synthetic resin of a multilayers structure (refer to, for example, JP-A-2003-220840). In this case, there is formed a thermoplastic synthetic resin member constituting an inner layer and an outer layer by high density polyethylene (HDPE) maintaining a strength necessary for the fuel tank and also strong at a fuel and constituting a middle layer as a barrier layer for preventing the fuel from being permeated therebetween.
In this case, at an opening portion 210, in order to attach a lid member 240 to the opening portion 210, a ring-like member 220 formed with a screw at an outer periphery thereof is integrally and fixedly attached to the opening portion 210. A face of the ring-like member 220 opposed to the lid member 240 is integrally and fixedly attached with a folded portion 212 of the opening portion 210 and a portion of the folded portion 212 is formed with a compression portion 213. A seal ring 250 is installed at inside of the compression portion 213 to seal an interval between the lid member 240 and the opening portion 210. However, the ring-like member 220 is formed by a synthetic resin and therefore, a strength thereof is low and it is difficult to ensure a sufficient rigidity against an external force.
Further, in order to fix the lid member 240 to the opening portion 210, a fixing member 230 in a ring-like shape and formed with a screw groove at inside thereof to the ring-like member 220, and therefore, time is taken for attachment, a predetermined length is needed at the screw portion, a height of the opening portion 210 is heightened, and a space is needed. Further, when the screw is excessively fastened tightly, since the ring-like member 220 is made of the synthetic resin, there is also a concern that the ring-like member 220 or the fixing member 230 is plastically deformed.